The present invention relates in general to the application of enclosures and designs thereof for isolating and protecting high voltage electrical apparati.
In electric utility networks, electrical power switchyards or utility stations and substations are commonplace to house and isolate electrical apparati such as power transformers, circuit breakers and switch gears which are essential for the transmission and distribution of electricity. In design, the transformers are conventionally connected to switching networks containing circuit breakers and switch gears to which the power lines are connected.
For example, a power transformer is a device for transferring electrical energy from one alternating-current circuit to another with a change in voltage, current, and/or phase. Commonly, a transformer consists of primary and secondary electrical windings that are magnetically linked via a ferromagnetic core (laminated or otherwise) in which the number of turns in each winding, hence the turns ratio between the windings, are varied so to manipulate the input and output characteristics of the transformer in accordance with Faraday""s law. Accordingly, a transformer, depending on the turns ratio of its windings, may be classified as a step-up or a step-down transformer in its ability to generate a higher or lower output (secondary) voltage relative to the input (primary) voltage, respectively. A transformer that steps-up voltage would step-down current and vice versa and it is this ability of the transformer to increase or decrease voltage and current which lends to its primary use for the economical transmission and distribution of electrical power. For instance, step-up transformers are often used to transfer electrical energy from the generators to the transmission lines (voltages as high as about 750,000 volts) while step-down transformers from the transmission lines to the end-users (voltages of about 120 to about 240 volts). Most commercial transformers used are capable of handling single-phase or multiple-phase alternating current circuits in that, for example, a three-phase transformer would consist of three single-phase transformers constructed onto a single core. The gauge and material of the wires and the size, material and design of the core will overall determine the power handling capacity of a transformer.
By definition, transformers can be classified as distribution and transmission or power transformers. A distribution transformer (in accordance with the U.S. Department of Energy and ANSI IEEE C57.12.80-1978 (subsection 2.3.1.1)) is a transformer with a primary voltage of about 480 V to about 35 kV, a secondary voltage of about 120 V to about 600 V, a frequency of about 55-65 Hz, and a capacity of either about 10 kVA to about 2500 kVA for liquid-immersed transformers or about 0.25 kVA to about 2500 kVA for dry-type transformers. A transmission or power transformer, in comparison, is a transformer capable of handling primary and secondary voltages as well as capacities greater than those of a distribution transformer.
Low voltage distribution transformers are currently commercially available with diverse attributes. Due to the relatively lower voltages and currents involved, the input and output terminals (for conductor connections) are congregated on a single surface (usually the front) of the transformer. To further improve safety, pad-mounted distribution transformers are typically supplied only with bushing wells with molded rubber components for insulating energized componentry and inserts and elbows for insulated conductor connections. These attributes are industrially referred to as the xe2x80x9cdead-frontxe2x80x9d design. Essentially, the dead-front layout is so designed or constructed to eliminate the exposure of and fully insulate current-carrying or energized parts that are normally exposed on the front of the transformer hence to simulate continuous and insulated conduction between the input or output conductor and the conductor connected to the windings of the transformer without any intervening functional componentry such as an insulator. In view of the above and the relatively lower hazards associated therewith, pad mounting of said distribution transformers at ground level with minimum containment measures is common practice in the industry. Examples of pad mounted, dead-front, low voltage systems are taught in Adkins et al. in Canadian Patent Application Number 2,217,619; Haubein in U.S. Pat. No. 3,784,727; Grannis in U.S. Pat. No. 3,841,032; Borgmeyer et al. in U.S. Pat. No. 4,533,786; Marusinic in U.S. Pat. No. 5,783,775; Reineke et al. in U.S. Pat. No. 6,066,802; and Book in U.S. Pat. No. 6,142,572 and Canadian Patent Number 1,287,868. These citations do not teach enclosure systems for live-front, high voltage transmission transformers.
Conversely, the significantly higher power ratings and voltages handled by transmission transformers render the use of the dead-front design impractical owing to the larger corona fields associated with high voltage conductor terminals and transmission transformers are currently only available in the live-front format in that glass or porcelain bushings with eyebolt or spade type terminals forming insulators are extended through the top side of the transformer so to insulate the transformer from the energized conductor terminals which insulator and conductor terminals and are fully exposed for connection to the conductors.
Transmission transformers are rated by their primary and secondary voltage relationship and their power carrying capability. For instance, a substation transformer rated at 66-13 kV and 5,000 kVA means that the primary or high voltage is 66,000 V, the secondary or low voltage is 13,000 V and the transformer has a power rating of 5,000,000 VA. Substation transformers, like most distribution transformers, consist of a core and coils immersed in oil in a steel casing. The oil serves as an insulator and coolant to maintain reliable operating temperatures, and certain transmission transformers incorporate pumps to circulate oil for better heat transfer, fins for the oil to circulate through and fans to force air across the fins.
To safeguard against the danger associated with prominently exposed energized componentry inherent with the live-front design of transmission transformers, the positioning of transmission transformers therefore requires pole mounting and/or isolation within large secured switch yard or substations. None of the above citations teach any enclosure system that can offer safety, security and cost savings that would be associated with pad mounting of live-front high voltage transmission transformers.
In view of the foregoing, the present invention provides a solution to containment of exposed high voltage electrical componentry, such as the insulator connections and the conductor terminals of a high voltage, live-front, transmission transformer, thereby reducing or eliminating the necessity for a conventional switchyard or substation and costs thereof.
An object of the invention is to provide novel means to contain and protect high voltage electrical apparati with exposed componentry thereby reducing or even eliminating the necessity for, and the high costs associated with conventional means for such containment and protection.
Another object of the invention is to provide a secure enclosure system for high voltage electrical apparati so to permit the placement of said high voltage electrical apparati at ground level.
According to a first aspect of the present invention there is provided a high voltage electrical handling device comprising a housing containing high voltage electrical componentry and at least one connector supported externally of the housing in communication with the high voltage electrical componentry, said at least one connector being at a high voltage and having a surrounding electrical corona field;
wherein the improvement comprises an enclosure comprising walls connected to the housing and surrounding said at least one connector at high voltage, spaced outside of the electrical corona field of said at least one connector.
The device preferably comprises a high voltage transmission transformer which may include a lower voltage connector and an upper voltage connector, each supported on a side of the housing and each having an enclosure surrounding the connector.
The connector is preferably spaced outwardly from the housing, supported at the free end of an insulator projecting from the housing in a live front configuration.
The connector may have a minimum phase to phase high voltage of at least 44,000 Volts, but preferably at least 60,000 Volts.
There may be provided at least one lower voltage connector supported on a first side of the housing and at least one upper voltage connector supported on a second side of the housing, both the upper and lower voltage connectors being enclosed by the enclosure.
In one embodiment, the enclosure comprises a first compartment surrounding said at least one lower voltage connector on the first side of the housing and a second compartment surrounding said at least one upper voltage connector on the second side of the housing.
The upper voltage connector may have a minimum phase to phase high voltage of at least 44,000 Volts, but preferably at least 60,000 Volts while the lower voltage connector has a lower voltage than that of the upper voltage connector. The upper voltage connector may have a maximum phase to phase high voltage of 250,000 Volts, but preferably a maximum phase to phase high voltage of 230,000 Volts.
The connector at high voltage is preferably only supported on a side of the housing with a top side of the housing being clear of any connectors.
The enclosure may include a door supported therein having locking means to restrict access by unauthorized persons. When there is provide a plurality of connectors at high voltage, the enclosure may include an access door supported therein in association with each of the connectors.
The access doors are preferably located in a primary common wall of the enclosure. An auxiliary door may also be located in a secondary wall of the enclosure.
In one arrangement, the enclosure is arranged for retrofitting existing high voltage electrical handling devices in the form a container having an open side for mounting adjacent the housing with said at least one connector at high voltage extending from the housing into the enclosure through the open side of the enclosure.
The enclosure is preferably arranged to be mounted onto the housing using threaded fasteners to avoid potential hazards incurred by welding.
When the enclosure includes an access door permitting access to an interior of the enclosure, there may be provided a secondary barrier supported within the enclosure for restricting access to said at least one connector through the access door, both the access door and the secondary barrier including locking means for restricting access to the surrounding electrical corona field of said at least one connector by unauthorized persons.
The secondary enclosure may comprise a grill permitting visual inspection therethrough, located outside of the electrical corona field of said at least one connector.
According to one aspect of the present invention there is provided a method of application and use of secure enclosure systems for attaching to high-voltage electrical apparati thereby containing and protecting exposed componentry thereof.
In one embodiment, the high voltage electrical apparati hereof are high voltage, live-front, transformers or high voltage circuit breakers.
In another embodiment, the inventors contemplate the use of a secure containment system of the present invention on a high voltage electrical apparati at ground level so to facilitate access and maintenance by authorized personnel without the need for aerial supports.
In a further embodiment, the use of a secure containment system of the present invention on a high voltage electrical apparati also mitigates the requirement for, or at least reduce the size of, a conventional switch yard or substation for securement of said high voltage electrical apparati thereby eliminating or reducing the costs required for same.
Another aspect of the present invention provides secure enclosure systems and designs thereof for attaching to high voltage electrical apparati thereby containing and protecting exposed componentry of said high voltage electrical apparati. Sufficient containment and protection are essential in the electric utility industry so to prevent personal or property damage that may result from accidental contact or tampering with exposed energized componentry of costly high voltage electrical apparati.
In one embodiment, the high-voltage electrical apparati is a high voltage, live-front, transmission transformer wherein the high-voltage phase-to-phase voltage is over about 44,000 V, up to about 250,000 V (phase-to-ground equivalent voltage of about 23,000 to about 144,000 V). Preferably, the high voltage phase-to-phase voltage is between about 60,000 V and about 230,000 V (phase-to-ground equivalent voltage of about 35,000 to about 133,000 V).
In another embodiment, the high voltage electrical apparati is a high voltage circuit breaker.
In a further embodiment, the enclosure system comprises one or more hollow container structures or compartments attached onto, and enclosing componentry exposed on, at least two sides of the high voltage electrical apparatus.
A further aspect of the present invention provides a high voltage, live-front, transmission transformer wherein the exposed componentry is positioned on more than one surface or face of the transformer. In one embodiment, the input conductor terminals of a high voltage, live-front, transmission transformer are segregated from the output conductor terminals with respect to their positioning on difference faces of the transformer.
In a preferred embodiment of the present invention, the secure enclosure system comprises two compartments, each essentially cuboid in shape, attached onto the front and one side of a high voltage, live-front, transmission transformer, enclosing the input (primary) insulators and connections and the output (secondary) connections, respectively, as shown in the accompanying figures.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating preferred embodiments of the invention are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.